As a transistor structure for decreasing the power consumption of semiconductor devices is proposed a structure called DTMOS (Dynamic Threshold Voltage MOSFET). The DTMOS is a transistor structure having the body electrodes of the respective transistors isolated from each other by the use of the STI and having the gate electrode and the body electrode short-circuited. In the DTMOS, when a transistor is ON, a large drive current can be obtained because the threshold voltage becomes relatively lower in comparison with the threshold voltage in the OFF state by the forward bias to the body electrode, and on the other hand, when the transistor is OFF, the leakage current can be maintained because of zero bias to the body electrode.
As a transistor structure for decreasing the body resistance of the DTMOS is proposed a structure called B-DTMOS (Bulk Dynamic Threshold Voltage MOSFET). The B-DTMOS is a transistor structure having the body electrodes of the respective transistors isolated from each other by the use of double wells formed in bulk substrate and trench device isolation. The B-DTMOS can easily control the thickness of the body region, and can much decrease the body resistance.
In the structure having the wells of the respective transistors isolated by the trench device isolation described above, the lead-out of the body electrode is a problem. As one of the countermeasures to this problem, a structure having the transistor portion and the body electrode leading-out portion isolated by shallow trench is proposed. In this structure, however, the body region below the shallow trench is reduced and has the resistance increased. The increase of the body resistance leads to the decrease of the operation speed and the increase of the power consumption.
The followings are examples of related: Japanese Laid-open Patent Publication No. 2004-311724; and Japanese Laid-open Patent Publication No. 2001-032051.
For higher speed and lower power consumption of the transistor, a semiconductor device of a structure which can decrease the body resistance, and its manufacturing method are expected.